You probably already know that all the angles in a triangle add up to 180 degrees.
From the triangle, you are given two angles already! Angle P=42.7 degrees and Angle O is a right angle=90 degrees.
Add the two angles up and you get 132.7!
After that, do 180 degrees - 132.7 degrees and you get 47.3 degrees for Angle N. Btw the answer is a.